MXPA01000385A - Thermocouple for use in gasification process - Google Patents

Abstract

An improved apparatus comprising a thermocouple for measuring the temperature in a gasification process is provided. The improvement comprises a sapphire envelope for enclosing at least a portion of the thermocouple. The sapphire envelope may be in the form of a sapphire sheath fitted over the thermocouple. The apparatus may also comprise a thermowell, with the sapphire envelope being provided by the thermowell.

Description

TER OCUPLA FOR USE IN THE GASIFICATION PROCESS FIELD OF THE INVENTION This invention relates generally to a thermocouple used in a gasification process and, in particular, to the use of sapphire to extend the useful life of the 5 thermocouples used in a process. of gasification. BACKGROUND AND SUMMARY OF THE INVENTION In high temperature gasification processes, a hot partial oxidation gas is produced from hydrocarbonaceous fuels, for example, carbon. In these processes, hydrocarbonaceous fuels are reacted with a reactive gas l P containing oxygen, such as air or oxygen, in a gasification reactor to obtain the hot partial oxidation gas. In a typical gasification process, the hot partial oxidation gas will be substantially composed of H2 CO, and at least one gas of the group h2O, CO2, H2S, COS, NH3, N2, Ar, together with particulate carbon, ash, and / or melted slag that commonly contains species such as Si02, AI2O3, and the oxides and oxysulfides of metals such as Fe and Ca. The partial hot oxidation gas in the gasification reactor will commonly be at a temperature ranging from 1, 700 ° F (927 ° C) at 3,000 ° F (1649 ° C), and more often from 2.00 ° F (1093 ° C) to 2,800 ° F (1538 ° C), and will be at a pressure so General, ranging from 1 atmosphere (98 kPa) to 250 atmospheres 824,500 kPa), and more frequently from 15 atmospheres (1, 470 kPa) to 150 atmospheres 824,500 kPa). Thermocouples are usually used to measure the temperature in these high temperature processes. Thermocouples can be used to measure the temperature in the gasification reactor. They can also be used to measure the temperature in steps of downstream processes in which the effluent cools and the particulate and gaseous contaminants are removed. Thermocouples are pairs of different metal cables that are connected at bends. The content of the cables must be different enough to allow a difference in the electrical potential between them. Except for the ends, the two cables are electronically isolated from one anr. Electrical insulation is usually provided with a tube of insulating material that has two holes that do not intersect and pass through the tube lengthwise. Typical insulation materials include high temperature and high purity ceramics such as alumina. When two cable splices have different temperatures, there is a difference in the electrical potential between them. The difference in the electrical potential and therefore the difference in temperature can be measured by a voltage measuring instrument placed on the thermocouple meter or alternatively through a voltage measuring instrument that sends signals by means of a transmitter placed on the circuit of the thermocouple. The choice of different metals used for the thermocouple will vary depending on, among r things, the range of temperatures expected to be measured. For example, one type of thermocouple commonly used under the conditions present in a gasification reactor has a cable containing platinum and about 30% rhodium and a second cable containing platinum and about 6% rhodium. r pairs of metals are used are used for different variations of different temperatures. An apparent problem with the use of thermocouples in the environment present in a gasification process, in particular the environment present in the gasification reactor, is the relatively short lifetime of the thermocouples. The relatively short life time is due in part to the extremely high temperatures and corrosive atmosphere that prevails during the operation of the gasification reactor. An unprotected thermocouple that is left in this environment quickly is attacked and becomes unusable. Said attack can be more severe when the thermocouple has contact with sulfur slags present in the reactor. To decrease this problem, thermocouples are commonly inserted in a refractory thermowell arranged along the outer wall of a gasification reactor or other surface! of external process. Refractory thermowells would include chromium-magnesium, high chromium, or similar resistant slag materials, and other refractory and non-refractory materials such as AI2O3, MgO, and stainless steel could be incorporated. When used in a gasification reactor, the thermocouple can be introduced by passing it through an opening in the external wall of the reactor pressure vessel. The thermowell can then pass through the corresponding opening in a refractory material, or series of refractory materials, which are commonly used to align the inner surface of the reactor pressure vessel. The thermowell can be extended in the open space of the reactor or it can be located at a slight distance from the interior of the reactor. Unfortunately, placing the thermocouple inside a thermowell has not given a total solution. Over time, the melted slag will open a gap in the thermowell. The gap is usually due to the effects of erosion and corrosion as well as thermal and / or mechanical pressure. However, the breach may also be due, in whole or in part, to an inherent failure in the thermowell. The gap, typically small at the beginning, allows the molten slag to enter the thermowell where it can be put in contact with the thermocouple, making it unusable.

Therefore, it would be beneficial to have means to increase the life time of the thermocouples used in the gasification process. According to one aspect of the present invention, an improved apparatus that ^ includes a thermocouple to measure the temperature in a gasification process. The improvement consists of a sapphire wrap to attach at least a portion of the thermocouple. The sapphire wrap may be in the form of a sapphire coating fitted over the thermocouple. The apparatus can also consist of a thermowell, with the sapphire wrap provided by the thermowell. According to another aspect of the invention, an improved apparatus for measuring the temperature in a gasification process comprises a thermowell and one or more thermocouples. The improvement comprises a sapphire wrap to attach at least a portion of at least one terrnocuple. The sapphire wrap may be in the form of a sapphire coating fitted over the thermocouple. The thermowell can contain at least one barrier layer composed of sapphire, with the sapphire envelope equivalent to the barrier layer composed of sapphire. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 represents a thermocouple produced according to an aspect of the invention. Figure 2 represents a segmented cross-sectional view of a portion 20 of the wall of the gasification reactor in which a thermocouple and thermowell are installed according to an aspect of the invention. DESCRIPTION OF THE ILLUSTRATIVE CHARACTERIZATIONS Gas mixtures that * mainly consist of H2, CO, and at least one gas of the group H2O, CO2, H2S, COS, NH3, N2, Ar, together with particulate carbon, ash 25 and / or melted slag which usually contains species such as SiO2, Al, 03, and the oxides and oxysulfates of metals such as Fe and Ca that are commonly produced by known partial oxidation processes in the reaction zone of a vertical refractory lined steel pressure vessel Free flow and downflow. An example of said process and pressure vessel are shown and described in U.S. Pat. co-assigned 5 No. 2,818,326 incorporated herein by reference. In such a process, the partial oxidation gas will typically be subjected to additional cooling and purification steps in which particulate contaminants, gaseous pollutants and water vapor are removed. The partial oxidation gas produced from said process will be commonly referred to, r depending on the chemical composition and intentional terminal use, such as synthesis gas, fuel gas, or reduction gas. The partial partial oxidation gas will be referred to in this document as covering all these potentials. The feed used to produce the partial oxidation gas comprises hydrocarbonaceous fuels. The term "hydrocarbonaceous" as used in this document to describe various suitable supplies is intended to include gaseous, liquid and solid hydrocarbons, carbonaceous materials, and related mixtures. In fact, virtually any organic material containing coal, fuel, or related pastes, can be included within the definition of the term "hydrocarbonaceous." For example, there are (1) pumpable fuels of solid carbonaceous fuels, such as particulate carbon dispersed in a vaporizable liquid carrier, such as water, liquid hydrocarbon fuel and related mixtures; and (2) solid-liquid-gaseous dispersers, such as atomized liquid hydrocarbon fuel and particulate carbon dispersed in a temperature moderating gas. The term "liquid hydrocarbon", as used in this document to describe 25 adequate liquid supplies, is intended to include various materials, such as liquefied petroleum gas, petroleum distillates and waste, gasoline, naphtha, kerosene, crude oil, asphalt, gas oil, residual oil, tarry oil and shale oil, oil derived from coal, aromatic hydrocarbons (such as benzene toluene, xylene fractions), coal tar, cyclic gas acerté from heat-catalytic fluid disintegration operations, furfural extracts from coking gas oil and related mixtures. "Gaseous Hydrocarbons", as used herein to describe suitable gaseous supplies, include methane, ethane, propane, butane, pentane, natural gas, coking homogen gas, refinery gas, acetylene gas, ethylene separation gas , and related mixtures. "Solid hydrocarbon fuels", as used in this document to describe adequate solid supplies, include, coal in the form of anthracite, bituminous, sub-bituminous: lignite; coke; residue derived from coal liquefaction; peat; shale oil; tars; Petroleum coke; pitch; particulate carbon (soot or ash); waste materials containing solid carbon, such as waters excluded; and related mixtures. The solid and gaseous liquid feeds can be mixed and used simultaneously; and these may include paraffinic, olefinic, aceylenic, naphthenic and aromatic compounds in any proportion. Also included within the definition of the term "hydrocarbonaceous" are oxygenated hydrocarbon organic materials including carbohydrates, cellulosic materials, aldehydes, organic acids, alcohols, ketones, oxygenated fuel oil, waste liquids and products derived from chemical processes. contains oxygenated hydrocarbon organic materials, and related mixtures.

In the reaction zone of a gasification reactor, the hydrocarbon fuel is contacted with an oxygen-free containment gas, ^ optionally in the presence of a temperature moderator. The reaction time will usually be in the variety of about 1 to 10 seconds, and preferably around 2 to 6 seconds. In the reaction zone, the contents will commonly reach temperatures in the range of approx. 1, 700 ° F (927 ° C) at 3,000 ° F (1649 ° C), and more usually in the range of approx. 2,000 ° F (1093 ° C) at 2,800 ° F (1538 ° C). The pressure will usually be in the range of approx. 1 atmosphere 898 kPa) at approx. 250 ^^ atmospheres (24,500 kPa), and more typically in the range of approx. 15 atmospheres 81, 470 kPa) at 15 * 0 atmospheres (14,700 kPa). As the partial oxidation gas proceeds downstream, the flow temperature will be reduced as the gas is subjected to several cooling, washing and other steps. According to the present invention, the temperature can be measured in several locations within the gasification process by thermocouples that have used a sapphire envelope in addition to that. The use of a sapphire wrapper according to the various characterizations of the invention, among other advantages, increases the useful life of the thermocouple on conventional thermocouples. In its various characterizations, ^ the sapphire wrapper will attach at least a portion of a thermocouple with which it is used. The use of the sapphire wrapper is advantageous in particular when it is used in conjunction with thermocouples placed so as to measure the temperature in the gasification reactor, as the detrimental effects of high temperatures, melted slag and corrosives prevail more in the reactor. In a characterization of the present invention, the sapphire wrapper is manifested in the form of a sapphire coating 24 that fits into at least one portion of a thermocouple. In this characterization, illustrated in Figure 1, a thermocouple 10 is provided. Thermocouple 10 is comprised of a pair of leads 12 and 14. The leads have different metal content so that a difference in electrical potential can develop between these when the thermocouple is exposed to a source of heat. Cables for example, may contain platinum and rhodium as their elements with the amounts of platinum and rhodium different in the two cables. Preferably one of the cables with approx. 30% rhodium while the other cable with approx. 6% rhodium. For both cables, the rest is platinum in principle. The wires are joined to each other in a hot splice 16 and a cold splice 18. The terms "hot" and "cold" are used because when used to measure the temperature of a gasification reactor, the hot splice 16 is Place closer to the heat source. You measure the difference between the electrical potential of the two cables, the representatives of the temperature being at the hot end. In fact, several means are known for those with ordinary skills in the art of measuring the difference in electrical potential. Any of these methods can be used in the present invention. For example, a voltage meter can be placed in the circuit of the thermocouple. Alternatively, and preferably, the cold junction 18 is placed in a temperature transmitter. The signal generated by the temperature transmitter can be transmitted to a control room or other location by the signal transfer means 20. With the exception of the hot and cold junctions, the two cables 12 and 14 are unlike one electronically isolated other. Since it is not critical how to isolate, in this characterization, the electrical insulation 22 is provided by a ceramic tube of high purity and temperature. Said ceramic tube can be made of, for example, alumina.

If the thermocouple described up to this point was used alone or in combination with a typical thermowell for the purpose of measuring the temperature of a gasification reactor, the thermocouple will succumb relatively quickly, as described, to the slag and other harmful materials present in the reactor. For this reason in the present characterization a sapphire coating 24 is provided to fit at least a portion of the thermocouple. The sapphire coating 24 is substantially resistant to attack by the slag and other products of the gasification process. The completed thermocouple, comprising the improved sapphire coating 24, can then be seen as having a distal end 26 adjacent to the hot splice 16. It is necessary that the sapphire coating 24 adjoin at least the splice 16.

Preferably, and as will be described later, the sapphire coating 24 will be of sufficient length so that before the molten slag reaches the top of the sapphire coating 24 the molten slag will cool down and reach a nominal or zero flow state. a gap will be formed at some other point in the sapphire coating. In the present characterization, the sapphire coating 24 is substantially tubular and has an attached end, which is equivalent to the distal end 26 of the thermocouple, and an open end 28; the opening at the open end 28 is capable of receiving and fitting into the existing thermocouple composed of two cables 12 and 14 and the electrical insulation 22 surrounding and insulating the cables. In a variation of the characterization, an enlarged sapphire connector 30 is provided at the attached end of the sapphire coating 24. the enlarged connector 30 increases the time the slag takes to penetrate the sapphire coating 24. The presence of the enlarged connector 30, in its simplest form, may be due to the fact that the lining may be inherently thicker at the attached end than at its sides.

In the present characterization, the sapphire coating 24 fits and covers only a portion of the existing thermocouple. The open end 28 advantageously must fit snugly in an electrical insulation 22. Foil of platinum wrapped around the electrical insulation 22 or wrapped around the inner surface of the coating 24 can be used with advantage to provide a good fit for the coating of Sapphire 24. In other characterizations, the sapphire coating 24 may extend and cover a larger portion, if not substantially all, of the existing thermocouples. Still in other characterizations, the sapphire can be used both to electronically insulate the two wires and to coat them. In said ^ Characterization, the sapphire coating 24 and the electrical insulation 22 will be composed of sapphire. In other characterizations of the invention, any of the described thermocouples having a sapphire coating 24 is advantageously combined with a thermowell. The combined device with advantage is used to measure the temperature in a process of gasification, in particular in a gasification reactor. Any thermocouple commonly used or subsequently developed by someone with ordinary skill in the art can be employed. These thermocouples would include chromium-magnesia barriers, high ^ Chromium, or similar materials resistant to slag, and can incorporate other refractory and non-refractory materials such as AI2O3, MgO and stainless steel. In a preferred thermowell, illustrated in combination with a thermocouple of the present invention in Figure 2, the thermowell is composed of an internal protection tube 62 and an external protection tube 64. The internal protection tube 62 can be formed to from a refractory of high density and low porosity, such as alumina or magnesia. A meltable refractory material, usually a refractory of high density and low porosity, is then poured around the protection tube 62 and is allowed to be positioned so as to fopne the outer protection tube around all but the opening of the inner protection tube 62. Preferably, this refractory material of high density and Low porosity is composed of chromium oxide or chromium-magnesium. In this characterization the thermocouple 10 is inserted into the thermowell, first at the distal end 26. The thermocouple 10 passes through a flanged reducer 76 and into the thermowell in contact with and coupled with the flanged reducer 76. The distal end 26 of the thermocouple 10 is positioned adjacent the tip 66 of the thermowell. Preferably, a space of approx. 0.125 inches (3.18x10'3 m) to approx. 0.25 inches (6.35x10"3 m) between the inner surface of the tip 66 of the thermowell and the distal end 26 of the thermocouple. * The ends upstream of the wires 12 and 14 of the thermocouple 10 extend to pass the end Rear of electrical insulation 22, and / or the sapphire coating 24 if the coating is abutting the electrical insulation 22. the cables pass through a pressure sealing fit 70. the pressure sealing fit 70 contacts a sleeve 72 that fits into a flange removable 74. The rim 74 is matted with the flanged reducer 76 which is coupled to the external steel wall 40 of the pressure vessel gasification reactor. The thermocouple 10 and thermowell assembly is held in place by bolting or camping the flange 74 to the flanged reducer 76 and similarly bolting or camping the flanged reducer 76 with the external steel wall 40 of the pressure vessel gasification reactor. The use of two separate connections provides an increase in efficiency in which a thermocouple 10 can be replaced without removing the thermowell. Instead of attaching the flanges, screw caps and nozzles or other connecting means can be used.

The thermowell, with or without the enclosed thermocouple 10, passes in succession directly through a hole in the steel wall 40 of the pressure vessel gasification reactor and then through an orifice aligned in the refractory 42 aligning the wall in the inside of the pressure vessel. The tip 66 of the thermowell is preferably placed so that it is removed from approx. 0.25 to about 0.75 inches (0.019m), preferably 0.5 inches (0.0127 m), from the face of the refractory 42 aligning the internal steel wall of the pressure vessel reactor. In this way, the average erosion is reduced in opposite manner when the tip 66 of the thermowell is placed evenly with the face of the refractory 42 or beyond the face of the refractory 42. The thermocouple 10 and the thermowell assembly placed in a gasification reactor exhibits an increase in slag resistance. In the gasification reactor the melted slag 50 is deposited outside on the inner walls of the refractory 42 aligning the inner steel wall of the pressure vessel reactor. The melted slag 50 will migrate towards the thermowell. As described, with the passage of time the effects of erosion and corrosion as well as thermal and / or mechanical pressure can cause a small gap in the tip 66 of the thermowell. When this occurs, the molten slag 50 will thereby migrate, moving to cold spots, through the gap and enter the internal protection tube 62, thereby coming into contact with the sapphire-coated thermocouple. Advantageously, with the sapphire coating 24, the cables 12 and 14 and the hot junction * 16 are protected against the melted slag 50 and its destructive effects. The melted slag 50 will continue to migrate into the inner protection tube 62 until it cools to the point where it achieves a zero or nominal flow state. Because of this, the sapphire coating 24 must be of sufficient length such that before the slag reaches the open end 28 of the sapphire coating 24, one of two things occurs: the melted slag 50 will achieve thermal equilibrium, it will cool down and achieve a state of zero or nominal flow; or a gap will form at some other point in the sapphire coating. This second possibility can occur first when the effects of erosion and corrosion as well as thermal and mechanical pressure cause the entire tip 66 of the thermowell to be removed. When this occurs, the sapphire coating 24 is deteriorated by all the effects of erosion and corrosion in the gasification reactor. Ultimately a gap is formed in the sapphire lining 24. With the wires 12 and 14 and the hot junction 16 unprotected, the thermocouple 10 fails. The selection of an appropriate length for the sapphire coating 24 is in the skill of someone with ordinary skill in the art who has knowledge of the characteristics of his specific processes, including the composition of temperature and gas, and having the benefit of his description. In other characterizations, one or more, and preferably three, thermocouples are inserted into a thermowell having at least a corresponding number of internal protection tubes 62. In said preferential characterization, the distal ends of one or more thermocouples are advantageously positioned at different points along the length of the thermowell. This arrangement provides an increase in the times between thermocouple and thermowell replacement. For example, in a characterization in which a total of three thermocouples are used, ultimately the slag entering the thermowell will first reach the thermocouple placed closer to the tip 66. This thermocouple will subsequently fail. Then the slag takes an additional amount of time to reach and cause failures of the second and third thermocouples. Thus, the process can work longer without the need to turn it off. While the accuracy provided by the second and third thermocouples is not as good as that of the first thermocouple, the difference does not pose a problem for process control as the readings of the second and third thermocouples can be corrected based on data collected before of the failure of the first thermocouple. In other characterizations, the sapphire wrap can be provided by using a thermowell made entirely or partly with sapphire. Said thermowell can have sapphire, preferably in the form of a sapphire fiber, intermixed throughout the thermowell. Said thermowell may also have at least one substantially continuous barrier layer composed of sapphire. These thermowells can be used with a thermocouple that does not have a separate sapphire coating. Alternatively, these thermowells can be used with sapphire-coated thermocouples.

In an illustrative characterization of a thermowell having at least one substantially continuous barrier layer composed of sapphire, an inner protection tube 62 of the thermowell can be formed with sapphire. In another characterization, a thermocouple having a sapphire coating can be used without a thermowell to measure the temperature in a gasification process.

However, this alternative is not preferential when the thermocouple is exposed to molten slag. While a sapphire coated thermocouple will withstand all the effects of erosion and corrosion in the gasification reactor for a longer time than a thermocouple with no sapphire protection, the use of a thermocouple with sapphire protection in conjunction with a thermocouple thermowell considerably increases the life time of the thermocouple used.

Claims (28)

1. to CHAPTER CLAIMING Having described the invention, it is considered as a novelty and, therefore, the content is claimed in the following: CLAIMS 1. In an apparatus comprising a thermocouple for measuring the temperature in a gasification process, the best comprises a sapphire wrap to attach at least a portion of said thermocouple.
2. 2. The apparatus of claim 1, said thermocouple comprising a pair of cables of different metal content joined at one end by a hot splice and at the other end by a cold splice, but on the other hand are electronically isolated one from the other. another by an insulation tube, wherein the sapphire wrapper is in the form of a sapphire skin having a closed distal end and an open end, said open end having been placed in a hot splice and at least a portion of the insulation tube.
3. 3. The apparatus of claim 1, which will comprise a thermowell, said thermowell surrounds said thermocouple and said thermowell comprises at least one barrier layer composed of sapphire.
4. 4. The apparatus of claim 1, which will comprise a thermowell, said thermowell 5 surrounds said thermocouple and said thermowell comprises an internal protection tube and an external protection tube, said internal protection tube being composed of sapphire, wherein said thermowell comprises said thermowell. Sapphire wrapper comprises said inner protection tube.
5. 5. The apparatus of claim 1, which will comprise a thermowell, wherein the gasification process employs a steel pressure vessel as a reactor. The cylindrical alienated refractory vertical free flow, and where the thermocouple placed in the sapphire coating is installed in the gasification reactor by passing it in succession directly through a flanged reducer and in the thermowell connected to the flanged redoubt, the thermowell is installed in the gasification reactor by first passing it through a hole in the steel wall of the pressure vessel and then passing through an orifice aligned in the refractory lining the wall inside the pressure vessel. The apparatus of claim 1, which will comprise a thermowell, said thermowell surrounding said thermocouple and said thermowell comprising an internal protection tube and an external protection tube. 7. The apparatus of claim 6, wherein the inner protection tube is composed of aluminum. 8. The apparatus of claim 6, wherein the inner protection tube is composed of sapphire. 9. The apparatus of claim 1, wherein the thermocouple is under the ambient pressure of the gasification process. 10. The apparatus of claim 1, wherein the temperatures to be measured vary from approx. 1, 700 ° F (927 ° C) at approx. 3,000 ° F (1649 ° C). 11. The apparatus of claim 2, wherein the pair of cables are composed of ^ platinum, rhodium, or related mixtures. 12. The apparatus of claim 2, wherein the isolation tube is composed of alumina. 13. The apparatus of claim 2, wherein the isolation tube is composed of sapphire. 14. In an apparatus for measuring the temperature in a gasification process, said W gasification process employs a reactor comprising a vertical free-flowing refractive lined pressure vessel, said apparatus comprising a thermowell and one or more thermocouples, said one or more thermocouples independently comprise a pair of wires of different metallic content joined at one end by a hot splice and at the other end by a cold splice but on the other hand are electronically isolated from one another by an insulation pipe; the improvement comprises a sapphire wrap to attach at least a portion of at least one thermocouple. The apparatus of claim 14, wherein the sapphire wrapper is in the form of a sapphire coating having a closed distal end and an open end, said open end having been placed in the hot splice and at least in the a 20 portion of thermocouple insulation tube. The apparatus of claim 14, wherein said thermowell comprises at least one rod layer composed of sapphire, wherein said sapphire shell comprises at least one barrier layer composed of sapphire. The apparatus of claim 14, wherein said thermowell comprises an internal protection tube 25 and an external protection tube, said inner protection tube being composed of sapphire, wherein said sapphire casing comprises said inner protection tube. 18. The apparatus of claim 14, said thermowell is installed in the reactor when first passing it through a hole in the steel wall of the pressure vessel and then passing it through an orifice aligned in the refractory lining the vessel. In the interior of the pressure vessel, one or more thermocouples are installed in the reactor as the thermocouples pass in succession directly through the flanged reducer and into the thermowell connected to the flanged reducer. 19. The apparatus of claim 15, said thermowell surrounding said thermocouple and ^^ said thermowell comprising an internal protection tube and an external protective tube. 20. The apparatus of claim 19, wherein the inner protection tube is composed of alumina. 21. The apparatus of claim 19, wherein the inner protection tube is composed of sapphire. 22. The apparatus of claim 14, said thermowell having one or more internal protection tubes, wherein the number of internal protection tubes is at least equivalent to the number of thermocouples, and wherein the distal ends of one or more tubes of protection are placed at different points along the length of the 0 thermowell. 23. The apparatus of claim 14, wherein one or more thermocouples are under ambient pressure of the gasification process 24. The apparatus of claim 14, wherein the temperatures to be measured vary from ca. 1,700 ° F (927 ° C) at approx. 3,000 ° F (1649 ° C). 25. The apparatus of claim 14, wherein the pair of cables are composed of platinum-rhodium or related mixtures. 26. The apparatus of claim 14, wherein the isolation tube is composed of alumina. 27. The apparatus of claim 14, wherein the isolation tube is composed of sapphire. 28. A thermocouple composed of a pair of wires of different metallic content joined at one end by a hot splice and at the other end by a cold splice but on the other hand are electronically isolated from each other by an insulating tube, the thermocouple which will comprise a sapphire wrap having a closed distal end and an open end, said open end having been placed in the hot splice and at least in a portion of the insulation tube.